Pilot light circuit for radio receivers and the like



A. C. MILLER Aug. 3, 1943.

PILOT LIGHT CIRCUIT FOR RADIO-RECEIVERS AND THE LIKE Filed NOV. 22, 1941 Cc C AWOo GU /17161 5% he?" A which eliminates the Patented Aug. 3, 1943 I m re-3o? .smrss I r .-i i [2,325,189 I @EOTLIGHT CIRCUIT'FiiR-RADKO t-RECEIVERSAND'IHELHCE f Ambrose Miller, Glenside, 1%.;assigrior tof Philco Radio and Television Corporation,Phila-. I delphiala, a'corporatio'n of Delaware.) j Application November lSMLoeri'aINor420;124 .i

coiaims. (c1. zeahrp f This invention relates pii'otli'gh t circuits for A. C.-D. C. receivers and more'particularly to a novel circuit for o erating the-pilot Light at supply line voltage? a c -.-B'ecaus'e of the frailty ply line Voltage incandescent lamps of the small wattage si'zes stu tabl'e for pilot "lights, and their resultant inability to withstand the shock of being turned on and off large numbers of times without premature burn out, it has been 'eustomary touse a6 volt pilotiight in AgCx-D. C. receivers in series with the heaters oithe vacuum tubes. This has been unsatisfactory, however,

'for on starting the incandescent filament comes quickly to its operating temperature, while the cathode heaters, which are of comparatively heavy wire, take considerable time to reach oper-' pedients have been attempted to solve this problem; for example, tapped cathode heater tubes,

ballast tubes, thermal relays and the like have been tried. As previously explained, supply line, e. g., 110-120 volt, pilot lights as a substitute for the troublesome series arrangement has found no favor as a solution up to the present time, since the 110120 volt lights of small wattage were always subject to the objection that quick burn outs due to the starting surge were inevitable.

It is one object of the present inventionto provide a novel pilot light circuit which enables the use of supply line voltage pilot lamps and above-mentioned objection thereto.

It is another object-of the invention to provide or theniaments irisripbetween-the resistort: and thecatno'de heaters 7 a circuit which gives reduced voltage for a pilot lamp on starting and substantially full voltage during operation of the radio set.

' In the accompanying drawing, the single figure is a diagrammatic illustration of the power sup-.

ply for a A. C.-D.C. radio receiver embodying the invention.

Referring specifically to the single figure, ther is shown a power plug I connected to the line wires 2 which include a switch 3. In series across fromthe invention. It will be apparent also that 7' pilot light a may be oezinected' from the junction ii totheotherside cit/he powerline. The voltage rating or this pilot-light is' prererably the supply line-voltage; Y 5

In "the operation or the circuit-,-.wh'en the switch 3 is closed,-the heaters d are coldand offer very low resistance to the how of current.

It, for example, these heaters normallydraw .150 am ere, the initial-current may rise as high as one-half ampere. Resistor {maybe approximate1y'50 ohms if the total voltage dropihrth'e heaters 4 at operatin curfent-is approximately equal to the: hue voltage, and the voltagetlrop in the resistor will be 7 /2 volts under operating conditions but may be 25' Volts under initial starting conditions. It is apparent that the Voltage drop acrossthe lamp8 will beline voltage minus the voltage drop in the resistor 5, and. un

der normal continuous 120 volt operation the pilot light will receivel20 volts minus7 /2 volts or 112 /2 volts, whereas under, starting conditions it will receive 120 volts minus 25 volts or 95 volts. It is therefore apparent that instead of receiving the full shock of the entire line voltage on cold starting, the lamp will receive only about voltage drop does not affect the operation of the heaters.

'In general, the resistor 5 may have a value such that the normal voltage dropthereacross is approximately 6 to 9 volts.

While in the circuit shown a single resistor' is used, the resistor might be divided and connected partin each line lead without departing other modifications of the invention are possible.

I claim: v I g 1. Inan A. C.-D. C. radio receiver in which the heater elements of the vacuum tubes are con nected in series across a source of power, and in which the heater current when the heaters are atoperating temperature is much lower'than when theheaters' are cold and the voltage drop' across the'heaters at ratedcurrent when the heaters are at operatir'igtemperature is approxi- 'mately equal to the voltage'of the source of power,

the combination of a resistor inseries with said heater-elements between one of the terminals of r the power source and'theheater elements, said resistor having a relatively low voltage dropv at said rated heater current, and an incandescent lamp having a Voltage rating substantially equal to the voltage of said'power source, said lamp being connected directly between the other terminal of said power source and the junction of said'resistor and the heater elements, whereby said incandescent lamp receivessubstantially less than line voltage when the tube heaters are first connected to the power source, and substantially full line voltage after the heaters have reached operating temperature.

2. A circuit for prolongingthe' life of a supply line voltage pilot lamp in a A; C.-D."C; receiver having series-connected cathode heaters, which comprises a resistor connected between one side of the power line and'saidheaters, the voltage drop at operating current across said resistor being of the order of a few volts, and a pilot lamp adapted to receive substantially tliefull line voltage connected directly betwe'entheother side of the power. line'ancl the junction of. said resistor and the heaters, whereby said lamp receives substantially less than line voltage when said heaters are first connected tothe powerline, vand substantially full line voltage after said heaters have reached operatingltemperature.

'3. A circuit fortprolongingthe life of a pilot light as defined in claim 2, in which the resistor has a'normal'voltage drop of approximately 6 to 9 volts. a r

.4. In an A; C.-D; Chreceiverin which the tube heaters are connected in series across a source of supply voltage, and in which said heaters have a lower resistance when cold than when at operating temperature, and require appreciable time to reach operating temperature,resistance means connected in series between the source of supply voltage'and the heaters, and a pilot lamp connected across the heaters, said lamp being adapted to receive substantially the full line voltage but subject to deleterious efiects'if full line Voltage is repeatedly applied, sald'resistance means having a materially greater voltage drop thereacross when the heaters are cold and a larger current is flowing than when the'heaters are at operating temperature.

5. In a radioreceiver, a plurality of tube heater elements connected to a power supply line, a pilot lamp connected across said supply line and adapted to receive. substantially the full line voltage,

- and means for materially reducing the voltage [AMBROSE 0; MrLLERL- 

